An undercut saw is a specialty circular power saw used by flooring installers for undercutting walls, moldings, door jams, and cabinetry so that new floors may be installed underneath. When the area is undercut using the saw, the new flooring is simply slid underneath the undercut area, which saves time and presents a visually appealing finish. Without an undercut saw, the flooring should be precisely cut to fit around these areas, which is laborious, costly, and often leaves unsightly gaps.
Most existing undercut saws have been constructed with a fixed blade guard assembly which consists of two telescoping parts that serve both as a blade guard and a height adjustment mechanism for the saw. As shown in FIG. 1, existing undercut saw 100 has a fixed blade guard assembly 120 consisting of a first top plate 140 and a second height adjustment skirt 160. Top plate 140 is fixedly joined to a rotary power unit 180 (commonly circular saw or grinder based power units). When movable guard 200 is retracted, the front of the top plate 140 preferably covers less than 180 degrees of the circular saw blade 220 so the saw 100 can operate in tight areas, such as inside corners. The back of the top plate 140 has a downwardly protruding back edge 240 which is typically semi-circular so that it can be precisely machined to a controlled outside diameter. The downwardly protruding back edge 240 of the top plate 140 mates with an inner surface 260 formed in the height adjustment skirt 160 which is also semi-circular. These two mating semi-circular parts may telescope up and down creating a height adjustment mechanism for existing undercut saw 100, while also providing a fixed blade guard assembly 120 surrounding the back of the blade 220. Base 450 is an integral part of height adjustment skirt 160. The bottom surface 451 of the base 450 forms the surface upon which the saw is placed while in use on a floor surface.
There are practical considerations of this existing height adjusting mechanism with respect to the fasteners used to hold the telescoping members at a desired height. The following is a history of various fastener combinations that have been used. In existing early model undercut saws, the fasteners used were carriage bolts socketed into square holes in the downwardly protruding back edge 240 of the top plate 140. The carriage bolts extending from the back of the top plate passed through slots in the height adjustment skirt forming threaded ends for mounting additional fasteners. First mounted on these threaded ends were so-called “guide washers”, which were specialized cast shapes designed to move within channels formed on a back surface of the height adjustment skirt. Last mounted on these threaded ends were wing nuts which were tightened down on the guide washers. The clamping force generated by the wing nuts pressured the guide washer against an outer surface of the height adjustment skirt, while the downwardly protruding back edge of the top plate was drawn against the inner surface of the height adjustment skirt by the pulling action of the carriage bolt. This clamping force frictionally held the top plate at a desired height within the height adjustment skirt.
In some more recent existing saws, one of which is shown in FIG. 1, the fasteners consisted of two threaded wing screws 280 which fastened into two tapped holes 300 in the downwardly protruding back edge 240 of top plate 140. Spring 340 and washer 360 were also mounted on wing screw 280 ahead of guide washer 320. Spring 340 and washer 360 pressure guide washer 320 against the curved outer surface 305 of the height adjustment skirt 160 within an outer guide washer channel 380. Thus, even when a wing screw 280 is loosened, pressure from the spring keeps the guide washer in its channel, providing at least some stability and guidance for the assembly during the adjustment process.
Existing guide washers have typically been generally trapezoidal cast shapes with a semi-circular inside surface 315 that precisely mates with the curved outer surface 305 within guide washer channel 380 of the height adjustment skirt 160. Two or three guide washers along with two or three sets of the aforementioned fasteners have been used on existing saws.
Since the rotary power unit 180 and rotatable circular saw blade 220 are fixedly assembled onto top plate 140, the height at which top plate 140 is frictionally held by the fasteners determines the height of cut. The top plate 140 may be frictionally held at any point in a vertical range of about one inch within the height adjustment skirt 160. This enables the height of cut for circular saw blade 220 to be set from floor level (i.e., flush to the floor or no height of cut) to a height of one inch above floor level.
The characteristics of these guide washer and fastener mechanisms for these existing height adjustment mechanisms are as follows: First, the guide washers sometimes do not frictionally hold the assembly together with sufficient force, and the top plate can shift within the height adjustment skirt as the saw is being used. Particularly as the user lifts and places the saw at various locations around a jobsite, the weight of the saw motor can cause the top plate to slip downward within the height adjustment skirt. As a result, in some places the undercut is not of sufficient height, and the user has to re-adjust and re-cut many areas.
Another characteristic of the existing fastening mechanisms and guide washers is that they do little to ensure that the top plate (and thereby the blade) is always parallel with the flat floor surface on which the saw rests during use. The blade should be kept parallel to the floor during undercutting so that the blade will not angle up or down in relation to the floor during a cutting operation. Keeping the blade parallel with the floor surface ensures that the height of undercut will be consistent. Otherwise, angling of the blade may cause the blade to wedge upward or downward. This can result in inconsistent height of cut. Angling of the blade can also bog down the motor during a cutting operation, or even cause the saw to kick back. An improved height adjustment mechanism that worked to prevent the top plate from being set at angles that are not parallel to the floor could prevent undesirable inconsistencies in the height of cut, and would promote safer usage by reducing the possibility of saw kickback.
The use of such existing telescoping height adjustment mechanisms fastened with guide washers and threaded fasteners was preferred for simplicity and low cost. However, various different mechanisms for setting and holding the height of cut for an undercut saw have been designed to address slippage and blade angling during use. Such designs have largely not been adopted because they were impractical for jobsite conditions or too expensive to manufacture. For example, U.S. Pat. No. 5,784,789 to Vargas discloses an undercut saw with a rack-and-pinion mechanism for height adjustment. The undercut saw of this disclosure employs a grinder based power unit. A circular saw blade is mounted onto its spindle. A cylindrical sleeve is mounted to the grinder motor to cover the rotating spindle. The sleeve has a rack formed in its back side. The sleeve is assembled into a base. The base holds the pinion. Thus, as the pinion is turned, the rack on the sleeve causes the power unit and blade to move up or down. The rack and pinion design ensures that blade will move up and down in a precise manner that keeps the blade parallel with the floor at all times. Two screws threaded through the base may contact the sleeve to fix the sleeve at a given height. The rack and pinion mechanism of saw proved too expensive for mass production, and was prone to binding from saw dust. As a result, it was not widely adopted.
U.S. Pat. No. 6,678,960 to Williams discloses an undercut saw with a housing which rests on a floor surface and itself has a fixed height. A tapped sleeve is mounted on top of the housing. A rotary motor with a central axis and a threaded case may be threaded into the tapped sleeve. The blade when mounted on the central motor armature axis may be moved up and down within the housing as the threaded case is turned within the tapped sleeve. The height is fixed by means of a jam nut also threaded onto the threaded case. This threaded adjustment mechanism ensures that the blade will be kept parallel to the floor at all times. The tapped sleeve and large threads on the motor housing of this design proved too expensive for mass production. This mechanism was also prone to binding from saw dust. Furthermore, the requirement that the blade be mounted on a central armature axis about which the entire assembly turned required that only motors such as routers having a single, central armature axis (without any offset spindle gear) could be employed. Such high RPM low torque motors are not powerful enough for large amounts of undercut sawing. In particular, a great deal of power is used by a saw to undercut an inside corner area. Williams' saw as disclosed could not perform such cuts, due to its bulky blade housing.
Other mechanisms for fixing the height of cut are disclosed within this application, including rack-and-pinion, frictional, interlocking, and lead screw mechanisms. With regard to Williams' lead screw mechanism, this is shown in FIG. 9 of Williams. Williams describes the mechanism as a “jack screw” 160 rotatably fastened onto an outer sleeve 63 on two bosses 151. When a knob 155 is turned, a teeter 161 having a lead nut 160 may be raised or lowered. Teeter 161 has an arm 162 with a thin end 67 which may pass through a slot through the case and engage a cavity 37 in the case 30. Spring 166 biases teeter into cavity 37. However, a separate tightening clamp 76 may close down the diameter of sleeve 63 to frictionally hold the case.
A lead screw mechanism such as Williams' “jack screw” generally requires a secondary holding mechanism besides the lead screw to hold the mechanism in position. Otherwise, an accidental bump on the lead screw knob or even vibration during use can cause the mechanism to shift unexpectedly. For Williams, the separate frictional mechanism of clamp 76 provides such a secondary holding mechanism.
Williams' jack screw design presents many manufacturing challenges that make it cost prohibitive. Much as with the threaded case of the embodiment previously discussed, Williams jack screw embodiment has a specialized motor housing having a precisely shaped outer “case” capable of sliding within a sleeve. This is not preferred as most commonly available power units come in the shape of a grinder or circular saw, and such power units have no such precisely shaped case. Furthermore, the tightening clamp used to frictionally hold the case within the sleeve is a large, tight tolerance slide fit mechanism which would entail high machining cost to produce. A lead screw mechanism which did not engage the case of the power unit would be preferred as just about any power unit could be employed.
A lead screw mechanism that worked in conjunction with existing low cost guide washers and fastener assemblies could provide additional support for the existing telescoping top plate and height adjustment skirt at a much lower cost. Such would be preferred as a low cost mechanism to provide the benefits of reduced slippage and angling of the blade. Williams teaches that “peripheral studs” (carriage bolt or wing screw fastener assemblies) or “wing nuts”, are “slow because several fasteners require adjustment” (Background of the Invention, paragraph 3).
Some existing undercut saws have been manufactured with a grinder motor as a power unit. As shown in FIG. 2, grinder motor 370 has a first axis of rotation 375 (long armature axis) operatively coupled to a perpendicular second axis of rotation 385 (spindle axis). A first handle 380 and switch 400 are typically located towards the back of the saw. A spindle housing 420 is typically located at the front of the saw. Spindle housing 420 is typically made out of aluminum, which is suitable for mounting a second, forward, movable handle for controlling the front of the saw.
Existing grinders typically have a second handle formed in the shape of a threaded post fastenable into tapped holes on either side of the aluminum spindle housing. Such threaded posts extend out quite a distance from either side of the spindle housing, which is preferred during a grinding operation to provide counter leverage for the user. However, such a handle assembly is not suitable for use in undercut saws. The extension of the handle prevents the saw from entering tight areas, such as inside corners.
For this reason, as shown in FIG. 2, existing undercut saws have been made with a narrow, plastic, U-shaped handle such as handle 440 for their second, forward, movable handle. U-shaped handle 440 is bolted into tapped holes 500 on both sides of spindle housing 420 with bolts 480 and lock washers 460. U-shaped handle 440 is preferably narrower than the width of top plate 140 below so that it does not prevent the saw from undercutting in tight areas, such as inside corners.
The use of bolts 480 and lock washers 460 to bolt a second, forward, movable handle, such as U-shaped handle 440, to spindle housing 420 is preferred for simplicity and low cost. The user can tighten down the bolts 480, and the lock washers 460 tend to hold the handle in place. The handle 440 can also be rotated backward (i.e., towards the first, back handle 380) whenever the saw is used to undercut in a low clearance area, such as underneath the toe-space of a cabinet.
However, if the user pushes excessively hard on U-shaped handle 440, it can rotate forward (towards blade 220). This is not preferred as this puts the user's hand in closer proximity to blade 220. Forward rotation is also not preferred, because whenever the handle is oriented at such an angle, the saw is less able to operate in tight areas, such as inside corners. Some added mechanism to prevent the forward handle of the saw from rotating forward from the normally preferred 90 degree angle would be a usability and safety improvement. A more solid handle and better mounts on the spindle housing could provide such an improvement. However, as previously explained, this handle should also be able to rotate backward for undercutting beneath a toe-space.
An undercut saw is primarily used to undercut walls, door jams, and cabinet areas so that new flooring materials may be fit underneath. Some flooring materials are very thin, such as sheet vinyl or linoleum. To provide the proper undercut for thin sheet vinyl, the undercut saw should cut flush to the floor. For this reason, in most existing saws, as shown in FIG. 3 (a bottom view of an existing undercut saw), fixed blade guard assembly 120 (comprised of top plate 140, and height adjustment skirt 160) and movable guard 200 are both open on the bottom. This allows the blade height to be adjusted as close to the floor as possible. However, the undercut saw is not always used to undercut flush to the floor. In many cases, such as for ceramic tile or hardwood plank flooring, the undercut is made higher, because the flooring material to be installed is thicker. In such cases, additional guarding structures may be added to increase safety. Such structures may be removably mounted onto the components comprising the fixed blade guard, or the movable blade guard, to cover more of the blade when the saw is not being used for undercutting to fit thin materials, such as sheet vinyl.
It is an object to provide an undercut saw with an improved mechanism for guiding the telescoping motion of the top plate and the height adjustment skirt so that during height adjustment the top plate tends to stay parallel with the base of the saw, thereby keeping the blade parallel to the floor surface upon which it is placed during use.
It is an object to provide an undercut saw with an improved mechanism for holding a top plate at a fixed elevation within a height adjustment skirt which is economical enough for mass production.
It is an object to provide an undercut saw with an improved handle fastening mechanism which may be more rigidly fixed to the spindle housing of a grinder motor, which may be adjusted to various angles, but stopped from certain angles that are not preferred.
It is an object to provide an undercut saw with additional safety mechanisms which may be removably mounted to the fixed and movable guards.